Gunmen have killed two members of staff of a Tamil-language newspaper in the northern Sri Lankan town of Jaffna, the paper's editor says.

Masked men wearing black burst into the offices of the Uthayan daily and opened fire indiscriminately, the paper's editor N Vidyadharan told the BBC.

Two other employees were seriously injured, he said. It is not clear who carried out the attack.

The attack comes amid mounting tensions between the military and Tamil rebels.

It took place on the eve of World Press Freedom Day, during which the lobby group, Reporters Without Borders, is due to add armed Tamil groups in Sri Lanka to its list of those threatening the media.

'Staff hid'

Mr Vidyadharan said the two employees died instantly.

"Hearing the gunfire, other employees either ran away or hid in different parts of the building," he told the BBC Tamil service.

Another member of staff blamed the attack on government-backed paramilitary forces.

Correspondents say Uthayan is sympathetic towards Tamil Tiger rebels. Jaffna, which has a predominantly Tamil population, is under government control.

International mediators have been scrambling to save a truce between the Tamil Tigers and the government which has been threatened by a surge in violence in the last month.

Earlier on Tuesday, the team monitoring a shaky 2002 ceasefire issued a clarification to a statement accusing government security forces of being involved in extra-judicial killings in the north and east.

The Sri Lanka Monitoring Mission now says the government has assured it that it is not aware of any such activities and the SLMM says it believes the government is sincere in this respect.

The shift came after SLMM head Ulf Henricsson was summoned to the foreign ministry.

More than 60,000 people have been killed in Sri Lanka since the rebels launched their campaign for a homeland for minority Tamils in the north and east of the country in 1983.